A vast majority of internal combustion engines employ a plurality of cylinders. Typically, each cylinder is provided with at least two valves (one for intake and one for exhaust). Some high performance engines have four valves per cylinder (a pair for intake and a pair for exhaust).
In all cases, the valves are operated against pressure generated by a spring which surrounds a corresponding valve stem and which is interposed between a shoulder or valve guide within the head and a spring retainer removably mounted on an end of the valve stem by a valve lock. In most instances, the valve locks are in the form of a split ring, each ring segment having an inner surface which is keyed to the valve stem and an outer surface which is tapered so as to limit the movement of the valve retainer relative to the valve stem in response to the pressure generated by the spring.
If it is desired to remove a valve spring or the valve itself, it is necessary to first remove the valve lock and the valve retainer. In order to remove the valve lock and the valve retainer, it is necessary to compress the spring far enough to disengage the valve retainer from the valve lock, whereby the valve lock segments are free for removal from their keyed engagement with the valve stem. Such compression of the valve spring is also required when installing or reinstalling the valve retainer and the valve lock.
While devices have, in the past, been developed for assisting in the compression of deep-pocket valve systems, such devices are in the form of large or bench-mounted units which, because of their size and construction, are often difficult to transport and cumbersome to use. A further disadvantage of these prior devices is that they necessitate the removal of the head from the engine block.